A former oil industry lobbyist has resigned as a White House aide after being accused of doctoring official US policy papers on global warming to play down the link between greenhouse gas emissions and global warming.

Philip Cooney, who was chief of staff of the White House council on environmental quality, quit his job two days after a report released by a watchdog group, the government accountability project, showed he had deleted some paragraphs and edited others drafted by government scientists.

The White House said his departure was "completely unrelated" to last week's disclosure. "Mr Cooney has long been considering his options following four years of service to the administration," said White House spokeswoman, Dana Perino. "He'd accumulated many weeks of leave, and decided to resign and take the summer off."

Mr Cooney, a lawyer with no science background, previously worked for the American Petroleum Institute, which lobbies for oil firms.

The government accountability project was unavailable for comment yesterday, but revealed last week that he changed the documents in a way that would be more beneficial to the oil industry. In a section which gauged how sound evidence was for climate change he inserted "significant and fundamental" before the word "uncertainties".

In another sentence which claimed: "The attribution of the causes of biological and ecological changes to climate change or variability is difficult," he included the word "extremely" before "difficult".

The White House insisted the changes did not violate an administration pledge to rely on sound science, and defended them as part of the normal review process.

But environmentalists say Mr Cooney's work is yet more proof that US policies favour the oil industry. In his first few months in office, President George Bush rejected the Kyoto protocol on climate change and at Tuesday's White House meeting with Tony Blair, he underlined the importance of further research. "I don't know if you're aware of this, but we lead the world when it comes to millions of dollars spent on research about climate change," he said. "It's easier to solve a problem when you know a lot about it."